Diffie-Hellman Program in C language

Question

I have written a program for Diffie-Hellman Program in C language I am getting following error while compiling the code. I am getting following error:

$gcc Diffie-Hellman.c -o Diffie-Hellman
/usr/bin/ld: /tmp/ccedcUj8.o: in function `power':
Diffie-Hellman.c:(.text+0x2e): undefined reference to `pow'
collect2: error: ld returned 1 exit status

Machine Spec : Linux Ubuntu 18.10 The Program is as below........

/* This program calculates the Key for two persons 
   using the Diffie-Hellman Key exchange algorithm */
#include <stdio.h> 
#include <math.h> 

// Power function to return value of a ^ b mod P 
long long int power(long long int a, long long int b, long long int P) 
{ 
    if (b == 1) 
        return a; 

    else
        return (((long long int)pow(a, b)) % P); 
} 

// Driver program 
int main() 
{ 
    long long int P, G, x, a, y, b, ka, kb; 
    
    // Both the persons will be agreed upon the 
    // public keys G and P 
    P = 23; // A prime number P is taken 
    printf("The value of P : %lld\n", P); 

    G = 9; // A primitive root for P, G is taken 
    printf("The value of G : %lld\n\n", G); 

    // Alice will choose the private key a 
    a = 4; // a is the chosen private key 
    printf("The private key a for Alice : %lld\n", a); 
    x = power(G, a, P); // gets the generated key 
    
    // Bob will choose the private key b 
    b = 3; // b is the chosen private key 
    printf("The private key b for Bob : %lld\n\n", b); 
    y = power(G, b, P); // gets the generated key 

    // Generating the secret key after the exchange of keys 
    ka = power(y, a, P); // Secret key for Alice 
    kb = power(x, b, P); // Secret key for Bob 
    
    printf("Secret key for the Alice is : %lld\n", ka); 
    printf("Secret Key for the Bob is : %lld\n", kb); 
    
    return 0; 
}

`pow` is a function of the math library. It is not enough to include ``, you must also link to the math library with `-lm`, so your compiler command is `gcc dh.c -o dh -lm`. — M Oehm, Apr 14 '19 at 13:19
(But I think you want a pure integer power function with `power`. In that case, [look here](https://stackoverflow.com/questions/101439/the-most-efficient-way-to-implement-an-integer-based-power-function-powint-int).) — M Oehm, Apr 14 '19 at 13:22

Diffie-Hellman Program in C language

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